i have tried and better tried to beat it but cant can anyone help please thanks, i bought it from steam

Can you be more specific? Are you stuck in the first or second part of the fight? Or are QTE's giving you trouble?

For starters, cast Yrden on the ground and let one of the tentacles be trapped on it (just not the big middle ones), then hack it off with your sword. Back off and repeat two more times.

http://www.youtube.com/watch?v=XukzWdvZ7H4

Also remember when you kill it, it has two tentacles that can be looted, not one! Double drops.

I don't know if you still need this answered, but here's how I dealt with the Kayran on dark mode:

The fight is pretty simple- you hack off three tentacles, then do a QTE, and cross the bridge( that will fall during the fight) to bomb the damn thing. The entire fight hinges on your ability to stay in the area of attack long enough to initiate a tentacle smash, but roll out before it makes contact with you.

NOTE: that some tentacles on the beast have a bulging, red mass- those are the targets. But how to reach them? Read on.

When I say left/right, I mean left/right from your perspective, sitting on your couch. Also note that the beast has two red mass tentacles on the left, and at least three on the right. See the image with the red mass tentacles, the beast has more tentacles than this.

Before the fight: I drank Mongoose, Rook, and Swallow. Used whetstone on Blasphemer silver sword (There aren't a lot of fights in the game where you would need to use a whetstone, but I used one for the Kayran fight because I wanted it over quickly). I had at least three Vigor.

Now the fight: the beast will attack with its' middle two tentacles, bringing them down on you- dodge to your LEFT, making sure you end up approximately in the area where the tentacle with the #1 red mass will land. Cast Yrden, you might get hit and lose a lot of HP, don't be disheartened. If you cast your trap right then the tentacle you were targeting should be trapped- jump back and hack that shit till it's off. NOW DODGE, DODGE, DODGE- dodge to the left- I found an area behind a pillar where I was relatively safe. Beware of falling rock.

Now roll out and cast Yrden on approximately the area where the #2 tentacle with the red mass should land, and roll to the left again. Hack the tentacle off.

Now cast quen and roll to the RIGHT- the beast is going to be mad, but it's predictable.

NOTE: when the beast is enraged, it proceeds with a sequence of tentacle smashing, and as such it never hits the same spot twice. Stay behind the smashing tentacles, not ahead of them.

Beware not to roll into the sticky goo.

Stop approximately at the area where the #3 red mass tentacle should land, cast Yrden and roll away before getting hit. Hack the tentacle. Dodge away to the back, and cast quen.

Now QTE time. Press the right button to jump on to the swinging tentacle. Press X to fill the bar. Press A when the button flashes or else you will smash into the wall and die. The fight repeats from the beginning so be vigilant during the QTE.

If you survive the QTE, you will notice a part of the bridge falling down. Start towards it, but beware of falling rock. Quen will not help against falling rock- dodge as best as you can, or get lucky.

Get to the end of the bridge- Geralt does some cool shit, the fight is won. Collect your hard earned booty, tell Sile she's useless.

Edited for clarity.